Dont run ast borrowck on mir mode #52083

spastorino · 2018-07-05T18:18:33Z

r? @nikomatsakis

Mark-Simulacrum · 2018-07-05T18:21:09Z

@bors try

bors · 2018-07-05T18:21:21Z

⌛ Trying commit 48765de with merge b27d9cf...

@nikomatsakis

…r=<try> Dont run ast borrowck on mir mode r? @nikomatsakis

nikomatsakis

Looks great. One nit.

nikomatsakis · 2018-07-05T18:22:11Z

src/librustc_borrowck/borrowck/mod.rs

@@ -89,6 +90,8 @@ pub struct AnalysisData<'a, 'tcx: 'a> {
 fn borrowck<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>, owner_def_id: DefId)
    -> Lrc<BorrowCheckResult>
 {
+    assert!(tcx.borrowck_mode() != BorrowckMode::Mir);


Nit: I would do

assert!(match tcx.borrowck_mode() { BorrowckMode::Mir => false, BorrowckMode::Ast => true, // etc });

i.e., spell out all the cases. That way, when we change the enum (as we plan to soon) we can be sure it is all correct.

Mark-Simulacrum · 2018-07-05T19:33:58Z

Try build failed; this needs a fix before perf can go forward.

Mark-Simulacrum · 2018-07-05T19:34:30Z

Wait, no, I misinterpreted the log. Ignore previous message.

Mark-Simulacrum · 2018-07-05T20:08:45Z

@rust-timer build b27d9cf

rust-timer · 2018-07-05T20:08:46Z

Success: Queued b27d9cf with parent 94eb176, comparison URL.

nikomatsakis · 2018-07-05T23:02:08Z

@bors r+

bors · 2018-07-05T23:02:09Z

📌 Commit 25266c1 has been approved by nikomatsakis

@nikomatsakis

…-mir-mode, r=nikomatsakis Dont run ast borrowck on mir mode r? @nikomatsakis

@ghost

Rollup of 9 pull requests Successful merges: - #51901 (Rc: remove unused allocation and fix segfault in Weak::new()) - #52058 (Use of unimplemented!() causing ICE with NLL) - #52067 (Visit the mir basic blocks in reverse-postfix order) - #52083 (Dont run ast borrowck on mir mode) - #52099 (fix typo in stable `--edition` error message) - #52103 (Stabilize rc_downcast) - #52104 (Remove unnecessary feature gate.) - #52117 (Dedupe filetime) - #52120 (ARM: expose the "mclass" target feature) Failed merges: r? @ghost

nnethercote · 2018-07-10T07:25:12Z

This was a decent win for performance, speeding up several NLL benchmarks, the best by 9%:
99b0ddb...4f0ca92

We now have apples-to-apples comparisons between the old and new borrow checkers, and the NLL dashboard shows that the new borrow checker is substantially slower. "Check" builds of most benchmarks are at least 10% slower, and two (tuple-stress and html5ever) are still as much as 20x slower; html5ever also has very high memory usage. (#52028)

…matsakis Remove migrate borrowck mode Closes rust-lang#58781 Closes rust-lang#43234 # Stabilization proposal This PR proposes the stabilization of `#![feature(nll)]` and the removal of `-Z borrowck`. Current borrow checking behavior of item bodies is currently done by first infering regions *lexically* and reporting any errors during HIR type checking. If there *are* any errors, then MIR borrowck (NLL) never occurs. If there *aren't* any errors, then MIR borrowck happens and any errors there would be reported. This PR removes the lexical region check of item bodies entirely and only uses MIR borrowck. Because MIR borrowck could never *not* be run for a compiled program, this should not break any programs. It does, however, change diagnostics significantly and allows a slightly larger set of programs to compile. Tracking issue: rust-lang#43234 RFC: https://github.com/rust-lang/rfcs/blob/master/text/2094-nll.md Version: 1.63 (2022-06-30 => beta, 2022-08-11 => stable). ## Motivation Over time, the Rust borrow checker has become "smarter" and thus allowed more programs to compile. There have been three different implementations: AST borrowck, MIR borrowck, and polonius (well, in progress). Additionally, there is the "lexical region resolver", which (roughly) solves the constraints generated through HIR typeck. It is not a full borrow checker, but does emit some errors. The AST borrowck was the original implementation of the borrow checker and was part of the initially stabilized Rust 1.0. In mid 2017, work began to implement the current MIR borrow checker and that effort ompleted by the end of 2017, for the most part. During 2018, efforts were made to migrate away from the AST borrow checker to the MIR borrow checker - eventually culminating into "migrate" mode - where HIR typeck with lexical region resolving following by MIR borrow checking - being active by default in the 2018 edition. In early 2019, migrate mode was turned on by default in the 2015 edition as well, but with MIR borrowck errors emitted as warnings. By late 2019, these warnings were upgraded to full errors. This was followed by the complete removal of the AST borrow checker. In the period since, various errors emitted by the MIR borrow checker have been improved to the point that they are mostly the same or better than those emitted by the lexical region resolver. While there do remain some degradations in errors (tracked under the [NLL-diagnostics tag](https://github.com/rust-lang/rust/issues?q=is%3Aopen+is%3Aissue+label%3ANLL-diagnostics), those are sufficiently small and rare enough that increased flexibility of MIR borrow check-only is now a worthwhile tradeoff. ## What is stabilized As said previously, this does not fundamentally change the landscape of accepted programs. However, there are a [few](https://github.com/rust-lang/rust/issues?q=is%3Aopen+is%3Aissue+label%3ANLL-fixed-by-NLL) cases where programs can compile under `feature(nll)`, but not otherwise. There are two notable patterns that are "fixed" by this stabilization. First, the `scoped_threads` feature, which is a continutation of a pre-1.0 API, can sometimes emit a [weird lifetime error](rust-lang#95527) without NLL. Second, actually seen in the standard library. In the `Extend` impl for `HashMap`, there is an implied bound of `K: 'a` that is available with NLL on but not without - this is utilized in the impl. As mentioned before, there are a large number of diagnostic differences. Most of them are better, but some are worse. None are serious or happen often enough to need to block this PR. The biggest change is the loss of error code for a number of lifetime errors in favor of more general "lifetime may not live long enough" error. While this may *seem* bad, the former error codes were just attempts to somewhat-arbitrarily bin together lifetime errors of the same type; however, on paper, they end up being roughly the same with roughly the same kinds of solutions. ## What isn't stabilized This PR does not completely remove the lexical region resolver. In the future, it may be possible to remove that (while still keeping HIR typeck) or to remove it together with HIR typeck. ## Tests Many test outputs get updated by this PR. However, there are number of tests specifically geared towards NLL under `src/test/ui/nll` ## History * On 2017-07-14, [tracking issue opened](rust-lang#43234) * On 2017-07-20, [initial empty MIR pass added](rust-lang#43271) * On 2017-08-29, [RFC opened](rust-lang/rfcs#2094) * On 2017-11-16, [Integrate MIR type-checker with NLL](rust-lang#45825) * On 2017-12-20, [NLL feature complete](rust-lang#46862) * On 2018-07-07, [Don't run AST borrowck on mir mode](rust-lang#52083) * On 2018-07-27, [Add migrate mode](rust-lang#52681) * On 2019-04-22, [Enable migrate mode on 2015 edition](rust-lang#59114) * On 2019-08-26, [Don't downgrade errors on 2015 edition](rust-lang#64221) * On 2019-08-27, [Remove AST borrowck](rust-lang#64790)

Remove migrate borrowck mode Closes #58781 Closes #43234 # Stabilization proposal This PR proposes the stabilization of `#![feature(nll)]` and the removal of `-Z borrowck`. Current borrow checking behavior of item bodies is currently done by first infering regions *lexically* and reporting any errors during HIR type checking. If there *are* any errors, then MIR borrowck (NLL) never occurs. If there *aren't* any errors, then MIR borrowck happens and any errors there would be reported. This PR removes the lexical region check of item bodies entirely and only uses MIR borrowck. Because MIR borrowck could never *not* be run for a compiled program, this should not break any programs. It does, however, change diagnostics significantly and allows a slightly larger set of programs to compile. Tracking issue: #43234 RFC: https://github.com/rust-lang/rfcs/blob/master/text/2094-nll.md Version: 1.63 (2022-06-30 => beta, 2022-08-11 => stable). ## Motivation Over time, the Rust borrow checker has become "smarter" and thus allowed more programs to compile. There have been three different implementations: AST borrowck, MIR borrowck, and polonius (well, in progress). Additionally, there is the "lexical region resolver", which (roughly) solves the constraints generated through HIR typeck. It is not a full borrow checker, but does emit some errors. The AST borrowck was the original implementation of the borrow checker and was part of the initially stabilized Rust 1.0. In mid 2017, work began to implement the current MIR borrow checker and that effort ompleted by the end of 2017, for the most part. During 2018, efforts were made to migrate away from the AST borrow checker to the MIR borrow checker - eventually culminating into "migrate" mode - where HIR typeck with lexical region resolving following by MIR borrow checking - being active by default in the 2018 edition. In early 2019, migrate mode was turned on by default in the 2015 edition as well, but with MIR borrowck errors emitted as warnings. By late 2019, these warnings were upgraded to full errors. This was followed by the complete removal of the AST borrow checker. In the period since, various errors emitted by the MIR borrow checker have been improved to the point that they are mostly the same or better than those emitted by the lexical region resolver. While there do remain some degradations in errors (tracked under the [NLL-diagnostics tag](https://github.com/rust-lang/rust/issues?q=is%3Aopen+is%3Aissue+label%3ANLL-diagnostics), those are sufficiently small and rare enough that increased flexibility of MIR borrow check-only is now a worthwhile tradeoff. ## What is stabilized As said previously, this does not fundamentally change the landscape of accepted programs. However, there are a [few](https://github.com/rust-lang/rust/issues?q=is%3Aopen+is%3Aissue+label%3ANLL-fixed-by-NLL) cases where programs can compile under `feature(nll)`, but not otherwise. There are two notable patterns that are "fixed" by this stabilization. First, the `scoped_threads` feature, which is a continutation of a pre-1.0 API, can sometimes emit a [weird lifetime error](rust-lang/rust#95527) without NLL. Second, actually seen in the standard library. In the `Extend` impl for `HashMap`, there is an implied bound of `K: 'a` that is available with NLL on but not without - this is utilized in the impl. As mentioned before, there are a large number of diagnostic differences. Most of them are better, but some are worse. None are serious or happen often enough to need to block this PR. The biggest change is the loss of error code for a number of lifetime errors in favor of more general "lifetime may not live long enough" error. While this may *seem* bad, the former error codes were just attempts to somewhat-arbitrarily bin together lifetime errors of the same type; however, on paper, they end up being roughly the same with roughly the same kinds of solutions. ## What isn't stabilized This PR does not completely remove the lexical region resolver. In the future, it may be possible to remove that (while still keeping HIR typeck) or to remove it together with HIR typeck. ## Tests Many test outputs get updated by this PR. However, there are number of tests specifically geared towards NLL under `src/test/ui/nll` ## History * On 2017-07-14, [tracking issue opened](rust-lang/rust#43234) * On 2017-07-20, [initial empty MIR pass added](rust-lang/rust#43271) * On 2017-08-29, [RFC opened](rust-lang/rfcs#2094) * On 2017-11-16, [Integrate MIR type-checker with NLL](rust-lang/rust#45825) * On 2017-12-20, [NLL feature complete](rust-lang/rust#46862) * On 2018-07-07, [Don't run AST borrowck on mir mode](rust-lang/rust#52083) * On 2018-07-27, [Add migrate mode](rust-lang/rust#52681) * On 2019-04-22, [Enable migrate mode on 2015 edition](rust-lang/rust#59114) * On 2019-08-26, [Don't downgrade errors on 2015 edition](rust-lang/rust#64221) * On 2019-08-27, [Remove AST borrowck](rust-lang/rust#64790)

Remove rustc_mir_borrowck attribute and use rustc_mir instead

0e31e2f

rust-highfive assigned nikomatsakis Jul 5, 2018

rust-highfive added the S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. label Jul 5, 2018

bors added a commit that referenced this pull request Jul 5, 2018

Auto merge of #52083 - spastorino:dont-run-ast-borrowck-on-mir-mode, …

b27d9cf

…r=<try> Dont run ast borrowck on mir mode r? @nikomatsakis

nikomatsakis requested changes Jul 5, 2018

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spastorino force-pushed the dont-run-ast-borrowck-on-mir-mode branch from 48765de to 79fb702 Compare July 5, 2018 18:27

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Do not run AST borrowck when -Zborrowck=mir

25266c1

spastorino force-pushed the dont-run-ast-borrowck-on-mir-mode branch from 79fb702 to 25266c1 Compare July 5, 2018 19:58

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nikomatsakis mentioned this pull request Jul 6, 2018

Want -Z borrowck=migrate to test planning migration to non-lexical lifetimes #46908

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Mark-Simulacrum added a commit to Mark-Simulacrum/rust that referenced this pull request Jul 7, 2018

Rollup merge of rust-lang#52083 - spastorino:dont-run-ast-borrowck-on…

54a440b

…-mir-mode, r=nikomatsakis Dont run ast borrowck on mir mode r? @nikomatsakis

Mark-Simulacrum mentioned this pull request Jul 7, 2018

Rollup of 9 pull requests #52123

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bors merged commit 25266c1 into rust-lang:master Jul 7, 2018

jackh726 mentioned this pull request Jun 3, 2022

Remove migrate borrowck mode #95565

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Dont run ast borrowck on mir mode #52083

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Dont run ast borrowck on mir mode #52083

Dont run ast borrowck on mir mode #52083

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